You can manage your social media posts, replies and scheduling with Hootsuite. Schedule your posts in advance across various social media sites such as Twitter, Facebook and so on. Here is what Wikipedia says about Hootsuite:
Hootsuite is a social media management system for brand management created by Ryan Holmes in 2008. The system’s user interface takes the form of a dashboard, and supports social network integrations for Twitter, Facebook, LinkedIn, Google+, Foursquare, MySpace, WordPress, TrendSpottr and Mixi.
Based in Vancouver, Hootsuite has over 500 staff located in Vancouver, San Francisco, New York, Hong Kong, London, Sydney, Singapore, and other countries. The company operates on a freemium model and has over 10 million users in more than 175 countries.
Here is an article on How To Use Hootsuite